Author Year Randomization Allocation concealment Blinding of outcome assessors Loss of follow-up (%)
Ang 2008 unclear unclear Yes 1.6
Hendrikx 2006 adequate unclear Yes 15
Hu 2011 adequate adequate Yes 0
Patel 2005 adequate adequate Yes 5
Stamm 2007 adequate unclear Yes 0
Yerebakan 2011 adequate adequate Yes 0
Zhao 2008 adequate unclear Yes 5.6
Table 2: Risk of bias assessment of included studies.